Tracking systems (also known as navigation systems) assist surgeons during surgeries that require the precise locating of instruments such as surgical instruments. Such surgeries include neurosurgery, spine, and orthopedic surgery. In one implementation, the tracking system tracks a position and orientation of the surgical instrument during the surgical procedure and often displays the position and/or orientation of the instrument on a monitor in conjunction with a preoperative image or an intraoperative image of the patient (preoperative images are typically prepared by MRI or CT scans, while intraoperative images may be prepared using a fluoroscope, low level x-ray or any similar device).
It has also been proposed that the surgical instrument be used free hand without the aid of a cutting jig, guide arm or other constraining mechanism to establish the location to which the cutting implement at the end of the instrument is applied. See, for example, U.S. Pat. No. 6,757,582 to Brisson et al. In one implementation, the tracking system typically employs a camera that detects a tracking device located on the surgical instrument. The tracking device has a plurality of optical markers such as light emitting diodes (LEDs) to determine the position and orientation of the surgical instrument. The position of the surgical instrument usually correlates to the coordinates of a working end of the instrument in three-dimensional space, the x, y, z or Cartesian coordinates, relative to the camera. The orientation of the surgical instrument means the pitch, roll, and yaw of the instrument. When both the position and the orientation of the surgical instrument are defined, the relative position of that instrument is known to the tracking system.
One type of surgical instrument is known as a “pencil-style” hand-held surgical instrument. The pencil-style hand-held surgical instrument is held by the hand of the user to perform a medical/surgical task on the tissue of the patient such as shape or remove tissue such as bone from a femur. The pencil-style handheld surgical instrument makes use of a telescoping nose for a depth degree of freedom. The pencil-style hand-held surgical instrument also makes use of two additional degrees of freedom which are provided via a pivoting gimbal mechanism. In one implementation, the instrument includes a portion having a threaded nose tube that translates linearly. A motor telescopes the nose tube using an elongated rotor with a long internal thread directly engaging the nose tube. The nose tube has an external thread on a proximal end, which directly interfaces with the rotor of the motor. As the rotor spins in one direction, the nose tube pulls in (due to the nose tube being keyed) and spinning in the opposite direction results in the nose tube pushing out. An example of such a pencil-style hand-held surgical instrument is disclosed in pending patent application U.S. Patent Application Publication No. 2013/0060278, filed Aug. 31, 2012, the entire disclosure of which is hereby expressly incorporated by reference.
Although the above has worked well, it is desirable to improve hand-held surgical instruments.